This invention relates generally to optical field flatteners and converters.
A field flattener or field converter is a known device that is commonly used to flatten or modify the field curvature of an optical system, wherein the term “field converter” refers to the general case of modifying one general curve to another and the term “field flattener” refers to the special case of converting a general curve to a plane. Optical imaging elements, including but not limited to lenses, mirrors, and diffraction gratings, typically introduce a degree of field curvature into an optical system, sometimes referred to as the Petzval curvature. The presence of this optical aberration causes the focus as a function of spatial field position to deviate from a common plane, typically in a predominantly spherical or aspherical fashion. Applicable detecting arrays, including CCDs and Multiple Quantum Well (MQW) structures, however, are for the most part constrained to planar geometries due to the inherent lithographic and epitaxial fabrication technologies. This mismatch between the image locus of optical systems aberration by field curvature and these planar detector arrays results in image degradation as a function of spatial field, particularly for large fields.
The classic approach to compensating for this fundamental mismatch is to make use of refractive solutions in lens design, chiefly the technique originating in 1872 with C. Piazzi-Smyth in which a negative field lens is placed adjacent to the image plane and is well known in the art. When a lens is placed near a focal plane it makes little contribution to the optical power, but can have a pronounced effect on the field curvature. This Piazzi-Smyth field flattener is a standard tool used in reducing the mismatch between curved image planes and planar detectors such as the classic photographic plates and solid-state detector arrays. While this refractive field flattener approach is effective for the types of field curvatures formed in typical lens systems, it is often not capable of correcting the large field curvatures generated in extremely compact or miniaturized optical imaging systems or those generated by many dispersive elements utilized in spectrometer or hyperspectral imaging systems.
Current field flattening and field conversion designs are either limited in their field flattening or field conversion capabilities, are too complex or costly to fabricate, or introduce unwanted optical aberrations.
There is therefore a need for an optical field flattener design that is more compact in physical size than current field flatteners.
Furthermore, there is also a need for an optical field flattener design that is optically faster than current field flatteners.
Furthermore, there is also a need for an optical field flattener design that is capable of correcting larger amounts of field curvature than current field flatteners.
Furthermore, there is also a need for an optical field flattener design that is self-corrected for optical aberrations.
Still further, there is also a need for an optical field flattener design that provides a combination of the characteristics described above with superior trade-offs than have been previously attainable.